松辽盆地大庆长垣伴生气中二氧化碳成因讨论  

Discussion about the CO_2 Origin in Associated Gas from Daqing Placanticline,Songliao Basin

作　　者：杨春[1] 刘全有[2] 米敬奎[3] 周庆华[3] 胡安平[1] 

机构地区：[1]浙江大学地球科学系,浙江杭州310027 [2]中国石化石油勘探开发研究院,北京100083 [3]中国石油勘探开发研究院,北京100083

出　　处：《天然气地球科学》2008年第2期244-249,共6页Natural Gas Geoscience

摘　　要：松辽盆地大庆长垣伴生气中δ13CCO2值为+3.65‰^+11.81‰,重于碳酸盐岩受热分解特征值(0±3‰),是国内发现最重的δ13CCO2值。通过对大庆长垣伴生气及松辽盆地其他地区浅层气中二氧化碳及与其共生甲烷碳同位素判别和数值模拟计算认为,造成长垣伴生气中的δ13CCO2值偏重的原因是CO2被细菌还原;CO2被细菌还原为CH4的过程中,在转化相同比例CO2的情况下,高分馏条件比低分馏条件下剩余CO2的δ13C值变重要快;要使剩余CO2的δ13C值表现出现今特征值,单一有机质热降解来源的CO2需要被细菌还原40%,碳酸盐岩热分解的CO2则只需6%;由于来自有机质热降解的二氧化碳对气藏组分产生较大影响,因此大庆长垣伴生气中CO2应主要来自碳酸盐岩热分解。The isotopically heavier carbon for CO2 in the associated gases from the Daqing Placanticline is observed in China, and the δ^13C CO2 values rang from ＋3.65‰ to ＋11. 81‰, more positive than those from thermal decomposition of carbonate with δ^13CCO2 = 0±3‰. According to the identification of the carbon isotopic composition of CO2 and symbiotic CH4 in the associated gas and shallow gases in the Songliao basin, the heavier δ^13CCO2 is caused by bacteria reduction. Meanwhile, based on numerical modeling, the δ^13CCO2 value changes fast for residual gas from the higher fractionation than from the lower during the bacteria reduction from CO2 to CH4. If the reduced CO2 has the similar δ^13C values to the present gas, the proportions of the reduced CO2 from the thermal degradation of organic matter and carbonate decomposition are up to 40% and 6%, respectively. Obvious change of gas composition in the associated gas in the Daqing Placanticline would happen if the CO2 compound were derived from organic matter. Therefore, the thermal decomposition of carbonate is the main source of CO2 in the associated gas of the Daqing Placanticline.

关 键 词：松辽盆地 伴生气 二氧化碳成因 碳同位素 细菌还原作用 

分 类 号：TE122.113[石油与天然气工程—油气勘探]